IEEE (Institute of Electrical and Electronics Engineers) 802.16 standards provide techniques and protocols to support a broadband wireless access. Standardization proceeded starting from 1999 and IEEE 802.16-2001 was approved in 2001. It is based on a single carrier physical layer called ‘WirelessMAN-SC’. Later, besides the ‘WirelessMAN-SC’, ‘WirelessMAN-OFDM’ and ‘WirelessMAN-OFDMA’ were added to the physical layer in IEEE 802.16a standards approved in 2003. After the IEEE 802.16a standards were completed, revised IEEE 802.16-2004 standards were approved in 2004. IEEE 802.16-2004/Cor1 (referred to as ‘IEEE 802.16e’, hereinafter) was finalized in the form of ‘corrigendum’ in 2005 in order to resolve and correct bugs and errors of the IEEE 802.16-2004 standards.
In a wireless communication system, control information with a size of relatively short information bits within tens of bits is exchanged between a transmitter and a receiver. Control information used in IEEE 802.16 standards includes a channel descriptor message defining the characteristics of a physical channel, a DL-MAP message defining an access to a downlink channel, a frame prefix including coding-related information of the DL-MAP message, and the like. An error generated during transmission of the control information may fatally affect reception of data. For example, if a transmission error is generated at the frame prefix, the DL-MAP message could not be decoded or an error would be generated for decoding of the DL-MAP message. Then, the receiver could not access downlink information or would access erroneous downlink information. Therefore, the control information should be transmitted with high reliability so that it may not affect system performance.
FIG. 1 illustrates an encoding process of the frame prefix based on the IEEE 802.16-2004 standards.
With reference to FIG. 1, a frame prefix of 24 bits is duplicated to form a block of 48 bits. The 48-bit block is subject to forward error correction (FEC) coding at a code rate of 1/2 to form a codeword of 96 bits. The codeword is subject to repetition coding four times to form a transport block of 384 bits. The 384-bit transport block is modulated and transmitted.
Duplicating the frame prefix before processing FEC coding is known to have a lower performance gain compared with repeating the codeword. In order to decode the duplicated frame prefix, generally, values obtained through soft-decision are combined to determine a value to be decoded, which, however, goes through a relatively complicated process compared with a Viterbi algorithm, a general convolutional code decoding method.
Thus, a method for effectively transmitting the control information which has a relatively short size and needs to be properly and accurately transmitted is required.